Warfarin

Brand names

• Apo-Warfarin
• Carfin
• Coumadin
• Panwarfarin
• Sofarin
• Taro-Warfarin
• Warnerin

Usage

To prevent and treat blood clot formation in patients suffering from heart, lung, and blood vessel disorders that could lead to heart attack, stroke, or other problems.

How it works

Warfarin blocks the action of vitamin K, a compound necessary for blood clotting.

Side effects

Serious

Allergic reaction (marked by wheezing; breathing difficulty; hives; or swelling of lips, tongue, and throat); bleeding into skin and soft tissue; abnormal bleeding from nose, gastrointestinal tract, urinary tract, or uterus; severe infection; excessive or unexpected menstrual bleeding; black vomit; bruises or purple marks on skin. Go to your local emergency department immediately.

Common

No common side effects have been reported.

Less common

Loss of appetite, unusual weight loss, nausea, vomiting, skin rash, diarrhea, cramping.

Possible interactions

Other medicaments:

Warfarin may increase the effects of:

• oral hypoglycemic agents.
• phenytoin (Dilantin) or fosphenytoin (Cerebyx).

Warfarin may decrease the effects of:

• cyclosporine (Sandimmune, others).
• phenytoin (Dilantin) or fosphenytoin (Cerebyx).

The following medicaments may increase the effects of warfarin:

• abciximab (Reopro).
• acarbose (Precose).
• acetaminophen (Tylenol, others-especially if more than 2,275 mg per week is taken).
• allopurinol (Zyloprim).
• alteplase (Activase) and is contraindicated if the prothrombin time is more than 15 seconds.
• amiodarone (Cordarone).
• amprenavir (Agenerase).
• androgens.
• aspirin and some other NSAIDs.
• azithromycin (Zithromax).
• bismuth subsalicylate (Pepto-Bismol).
• some calcium channel blockers (various) have been associated with an increased risk of stomach and intestine (gastrointestinal) hemorrhage. This risk may be exacerbated by warfarin use.
• carbamazepine (Tegretol).
• cephalosporins.
• chloral hydrate (Noctec).
• chloramphenicol (Chloromycetin).
• cimetidine (Tagamet).
• ciprofloxacin and other quinolone antibiotics.
• cisapride (Propulsid).
• clarithromycin (Biaxin).
• clofibrate (Atromid-S).
• clopidogrel (Plavix).
• cloxacillin (various).
• cotrimoxazole (Bactrim).
• COX II inhibitors (celecoxib and rofecoxib).
• dextrothyroxine.
• dirithromycin and other macrolide antibiotics.
• disopyramide (Norpace).
• disulfiram (Antabuse).
• enoxaparin (Lovenox).
• erythromycin (various).
• felbamate (Felbatol).
• fluconazole (Diflucan).
• fluoxetine (Prozac).
• fluvastatin (Lescol) and perhaps similar medicaments.
• fluvoxamine (Luvox).
• fosphenytoin (Cerebyx) or phenytoin (Dilantin).
• gemfibrozil (Lopid).
• glucagon.
• heparin (various).
• HMG CoA-reductase inhibitors.
• influenza vaccine (various).
• isoniazid (INH).
• itraconazole (Sporanox).
• ketoconazole (Nizoral).
• mesna (Mesnex).
• methyltestosterone (any 17-alkylated androgen).
• metronidazole (Flagyl).
• miconazole (Monistat).
• minocycline.
• nonsteroidal anti-inflammatory medicaments.
• omeprazole (Prilosec).
• orlistat (Xenical).
• paroxetine (Paxil).
• pravastatin (Pravachol).
• propafenone (Rythmol).
• propranolol (Inderal).
• propoxyphene (various).
• quinidine (Quinaglute).
• quetiapine (Seroquel).
• ranitidine (Zantac).
• ritonavir (Norvir) and perhaps other protease inhibitors.
• salicylates (aspirin, etc.).
• sertraline (Zoloft).
• simvastatin (Zocor).
• streptokinase.
• sulfinpyrazone (Anturane).
• sulfonamides.
• tamoxifen (Nolvadex).
• tamsulosin (Flomax).
• terbinafine (Lamisil).
• testosterone (various).
• tetracyclines.
• thyroid hormones (various).
• thrombolytic medicaments (such as alteplase).
• tramadol (Ultram).
• trastuzumab (Herceptin).
• tricyclic antidepressants
• vancomycin (Vancoled).
• vitamin E.
• zafirlukast (Accolate).
• zileuton (Zyflo).
• zotepine (Nipolept).

The following medicaments may decrease the effects of warfarin:

• antithyroid agents (various) by decreasing prior high rates of clotting factor metabolism.
• azathioprine (Imuran).
• barbiturates.
• birth control pills (oral contraceptives).
• carbamazepine (Tegretol).
• chlordiazepoxide (Librium).
• cholestyramine (Questran).
• estrogens (various).
• ethchlorvynol (Placidyl).
• glutethimide (Doriden).
• griseofulvin (Gris-PEG).
• phenobarbital (various).
• phytonadione (vitamin K).
• primidone (Mysoline).
• rifampin (Rifadin).
• spironolactone.
• sucralfate (Carafate).
• thiazide diuretics.
• vitamin K.

Foods:

A larger intake than usual of foods rich in vitamin K may reduce the effectiveness of this medicament and make larger doses necessary. Foods rich in vitamin K include asparagus, bacon, beef liver, cabbage, fish, cauliflower and green leafy vegetables. Vitamin C in high doses has some conflicting reports of warfarin resistance. Vitamin E (high dose) may increase risk of bleeding.

Herbal medicines or minerals:

Because many herbal products are extracts from plants with a variety of active compounds in addition to those listed on the label-and since many compounds can have activity as anticoagulants-herbal medicines in general should not be combined with warfarin.
Specifically, angelica root, anise, borage seed oil, devil's claw, papain, ginseng, ginger, ginkgo, horse chestnut, alfalfa, red clover, clove oil, feverfew, passionflower herb, salvia root, willow bark, cinchona bark, turmeric and garlic may also change clotting, so combining those herbals with these medicines cannot be recommended. Talk to your doctor before taking any herbal medicine with warfarin.

Alcohol:

Limit alcohol to one drink daily. Note: Heavy users of alcohol with liver damage may be very sensitive to anticoagulants and require smaller than usual doses.

Tobacco smoking:

Heavy smokers may require relatively larger doses of this medicament.

Discontinuation:

Do not stop this medicament abruptly unless abnormal bleeding occurs. Ask your physician for guidance regarding gradual reduction in dose over a period of 3 to 4 weeks.

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